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Diabetic Retinopathy: The Enemy from Within

In recent years, the world has recognized diabetes as one of the most daunting challenges posed by chronic diseases. The number of sufferers worldwide is currently estimated to be about 135 million; this number is expected to rise to almost 300 million by year 2025. The World Health Organization (WHO) and the Department of Health (DOH) estimate that diabetes affects between 5 and 10 million Filipinos at present, more than half of which are not aware that they have the disease. Thus, with the majority of patients being unaware of the primary disease, it is not surprising that knowledge about the complications of diabetes, including retinopathy is poor.

Diabetic retinopathy is the leading cause of blindness and visual disability among adults in economically developed societies. It occurs when the tiny blood vessels (capillaries) nourishing the retina (the light-sensitive tissue at the back of the eye that captures light and relays information to the brain, much akin to what a film does in a camera) get damaged by the high blood sugar levels in the blood.

Diabetic retinopathy usually affects both eyes. It follows a gradually worsening course beginning with the relatively milder non-proliferative stages wherein worsening damage to the retinal blood vessels results to vascular blockage and poor nourishment of several areas of the retina.

These poorly nourished areas in the retina in turn, send out signals to produce new blood vessels in an attempt to improve nourishment, leading to the next and, more severe proliferative stage. In this stage, new blood vessels grow along the retina and into the clear gel that fills the inner eye (the vitreous). These new blood vessels may even grow and extend into the front part of the eye. However, these new blood vessels are abnormal and fragile and thus, they have a tendency to bleed. When bleeding inside the eyes occurs, severe loss of vision or even blindness may ensue. Eventually, scarring may follow. As such, visual prognosis worsens with the severity and extent of eye involvement.

Who is at risk for Diabetic Retinopathy?
All diabetics, regardless of type are at risk. The risk likewise increases with the duration of diabetes mellitus (DM). In Type 1 DM (previously known as juvenile-onset DM), about 25% of patients have retinopathy after 5 years, 60% after 10 years, and 80% after 15 years. Proliferative diabetic retinopathy (PDR) is present in 1 out of every 4 patients with a 15-year history of the disease.

In Type 2 DM (previously known as adult-onset DM) patients, PDR develops in 2% of patients who have diabetes for less than 5 years; this number increases to 25% in patients with a disease duration of 25 years or more. Some reports indicate that in Type 2 DM, about 21% of patients have retinopathy at the time of diagnosis of diabetes and their retinopathy is believed to have begun at least 6.5 years before diagnosis.

During the early stages of diabetic retinopathy or even in the more severe stages, patients may have no blurring of vision or any visual symptoms at all.

Some of the visual symptoms may include:
• Seeing tiny specks floating
• Blurring or loss of vision
• Dark or red streaks obscuring vision due to bleeding inside the eye
• Dark or empty spot at the center of vision
• Poor night vision or difficulty adjusting from bright to dim light
• Seeing flashes of light
• Eye redness or pain due to elevated pressure inside the eye

Blurring or Loss of Vision in Diabetic Retinopathy

Blurring of vision or visual loss in diabetic retinopathy usually results either from bleeding from the abnormal and fragile blood vessels that grow during the proliferative stage, or from the leakage of fluid in the center of the macula, the part of the eye where we see the clearest and the sharpest.

Patients may initially see spots, specks, dark or red streaks floating in their vision when bleeding inside the eye occurs. In some instances, these “floaters’ may spontaneously decrease in number, size or even disappear. But this should not be a reason for the patient to be complacent as more serious and potentially blinding complications of PDR may ensue if interventions are not instituted promptly.

When fluid leaks in the macula, it swells, blurring vision. While about half of patients with proliferative retinopathy have macular edema, it can occur at any stage of the disease. Patients and eye healthcare providers must be wary that significant macular edema may be present even without the patient experiencing bothersome blurring of vision.

Other possible causes of blurring or loss of vision in diabetic retinopathy include separation of the retina from its underlying attachments (retinal detachment) and scarring.

Time to See Your Eye Doctor
As mentioned previously, diabetic retinopathy often has no warning signs. Patients usually have false confidence that they don’t have the disease because they can see perfectly well. Early detection of retinopathy increases the patient’s chances against developing severe visual loss or blindness, for which regular eye examinations are deemed essential.

Diabetics are being advised to seek complete eye examination (including examination of the retina with the pupils of the eyes dilated) at least once a year. Diabetic retinopathy may pose a problem among pregnant patients with diabetes, thus they should have a comprehensive eye examination as soon as possible. Additional examination may be recommended throughout the duration of pregnancy.

Patients should see their eye doctor promptly should they experience any of the signs and symptoms mentioned above.

Screening and Diagnosis
During a patient’s visit to an eye doctor’s clinic, several examinations are carried out in order to detect diabetic retinopathy. These may include:

1. Visual Acuity testing to check how well a patient sees at various distances.
2. Slit-lamp examination — also called biomicroscopy, is done to check for abnormalities in the front parts of the eyes like bleeding, growth of new blood vessels and cataract.
3. Tonometry — using a special instrument, the pressure inside the patient’s eyes is measured.
4. Dilated Pupil Examination — drops are instilled into the patient’s eyes so that the pupils would enlarge or widen (dilate). Using special instruments, including lenses, the patient’s retina and optic nerve are thoroughly scanned for disease.

The eye doctor will look for the following signs of diabetic retinopathy:
1. Optic nerve and nerve tissue changes
2. Changes in blood vessels, such as closures, beadings or loops
3. Abnormal blood vessels (microaneurysms/new blood vessels)
4. Leaking from the abnormal blood vessels
5. Retinal bleeding (hemorrhage)
6. Macular swelling (edema)
7. Deposition of fats and proteins (exudates) in the retina
8. Cotton-wool spots signifying poor delivery of oxygen in certain areas of the retina
9. Bleeding into the vitreous gel
10. Scarring
11. Retinal detachment.

When indicated, the eye doctor might request for additional examinations like Fluorescein Angiography (FA) and Optical Coherence Tomography (OCT).

Fluorescein Angiography is a procedure wherein dye is injected into a vein in the patient’s arm to easily identify the retinal blood vessels and the accompanying abnormalities. Using a special camera, photographs are taken while the dye is in circulation, providing the eye doctor with vital images showing leakage, bleeding, blockage and status of retinal blood flow. These images may be used as a guide in treating patients, particularly for macular edema.

Optical Coherence Tomography is a non-invasive imaging tool, providing high resolution images of the retina to help measure retinal thickness and detect leakage of fluid into retinal tissue. This examination is useful for both diagnostic purposes and for monitoring effectiveness of treatment.

Complications
The growth of the new blood vessels during the proliferative stage of diabetic retinopathy does not restore nourishment to the retina. Instead, they may bring about the following complications:

Vitreous Hemorrhage (Bleeding) — the new blood vessels can bleed into the vitreous gel and the severity of the resulting visual symptoms correlates well with the amount of blood in the vitreous cavity. Vitreous hemorrhage by itself usu¬ally does not cause permanent visual loss. The blood often clears up spontaneously, within weeks or months, and the patient’s vision may return to its previous clarity in the absence of significant retinal damage.

Traction Retinal Detachment – left unabated in their early development, the proliferation of these new blood vessels are accompanied by the growth of fibrous (scar) tissue.When the scar tissue shrinks, it may tug on the underlying retina and lift it away from its underlying attachments. Retinal detachment may cause blank or blurred areas in the patient’s visual field, even blindness in severe cases.

Neovascular Glaucoma – results when the outflow of fluid within the eye is impeded by the growth of the new blood vessels on the iris (the brown part of the eye). As a consequence, the pressure inside the eye builds up, damaging the optic nerve. Neovascular glaucoma is one of the most severe and potentially blinding outcomes of PDR.

Treatment
When indicated, there are two main treatment modalities for diabetic retinopathy – photocoagulation (laser treatment) and vitrectomy. While these interventions are effective and slow or even stop the progression of the disease and loss of vision for some time in many cases, they are not a cure and the benefits might not be realized immediately. Because diabetes continues to affect the body, further retinal damage and vision loss may still be experienced by the patient at a later time. Therefore, additional treatments may be recommended, even when the patient has already undergone certain interventional procedures.

Photocoagulation (Laser treatment) – is an outpatient procedure, usually done with anesthetic eye drops. The goal of treatment is to control the leakage of blood and fluid in the retina, as well as the growth of new blood vessels, in an attempt to slow down the progression of diabetic retinopathy and, consequently, loss of vision.

Photocoagulation may be recommended in the following cases:
• Macular edema
• Severe non-proliferative diabetic retinopathy especially among Type 2 diabetics and poorly compliant patients
• Proliferative diabetic retinopathy
• Neovascular glaucoma

Vitrectomy – may be indicated for massive bleeding inside the eye that does not clear up. This may help improve the patient’s vision and allow the application of the needed laser treatment. This procedure is also done to remove the scar tissue pulling on the retina. Vitrectomy can be done under local or general anesthesia.

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